Simulated radiative forcing from contrails and contrail cirrus

Chen, Celia; Gettelman, Andrew

doi:10.5194/acp-13-12525-2013

Cited by 57 publications

(87 citation statements)

References 40 publications

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“…The treatment of aviation soot in the parameterization can also lead to very different conclusion of their impact. The low radiative forcing of aviation BC found in this study is consistent with Chen and Gettelman (2013), who show that a larger forcing could be simulated when a higher heterogeneous ice nucleation efficiency for BC aerosols is assumed. Furthermore, uncertainties can also result from the assumed particle size of aviation aerosols, which is reported in Chen and Gettelman (2013).…”

Section: Discussionsupporting

confidence: 78%

“…For example, for 2050 aviation emissions, we use the background meteorologies from years 2049, 2050, 2051 and 2052 to drive CAM5-SD to form an ensemble. This modeling strategy is employed instead of transient simulations because Chen and Gettelman (2013) the expected radiative forcing of aviation emissions when it was in a free running mode which would not allow us to effectively obtain forcing of statistical significance. The radiative forcing is then estimated from 80 simulated years.…”

Section: Modeling Framework and Background Meteorologymentioning

confidence: 99%

“…Following the methodology described in Gettelman and Chen (2013) and Chen and Gettelman (2013), CAM5 with specified dynamics (CAM5-SD) is employed for this study. Future background meteorology is obtained from fully coupled simulations using Community Earth System Model (CESM) under representative concentration pathways (RCPs) with radiative forcing in 2100 of 4.5 and 8.5 W m −2 (van Vuuren et al, 2011), hereafter RCP4.5 and RCP8.5.…”

Section: Modeling Framework and Background Meteorologymentioning

confidence: 99%

“…Nevertheless, it is a challenge to quantify the radiative forcing of contrail cirrus since this requires accurately accounting for the spreading of contrails. Based on some recent studies using general circulation model simulations, Burkhardt and Kärcher (2011) estimated present-day contrail cirrus radiative forcing of 31 mW m −2 , Chen and Gettelman (2013) C.-C. Chen and A. Gettelman: Future aviation radiative forcing Aircraft also emit various aerosols, such as sulfate and black carbon (BC, or soot). In addition to directly absorbing and reflecting radiation, sulfate and BC can alter cloud properties, such as drop and crystal concentration, and cloudiness in the troposphere.…”

Section: Introductionmentioning

confidence: 99%

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Simulated 2050 aviation radiative forcing from contrails and aerosols

Chen

Gettelman

2016

Atmos. Chem. Phys.

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Abstract. The radiative forcing from aviation-induced cloudiness is investigated by using the Community Atmosphere Model Version 5 (CAM5) in the present (2006) and the future (through 2050). Global flight distance is projected to increase by a factor of 4 between 2006 and 2050. However, simulated contrail cirrus radiative forcing in 2050 can reach 87 mW m −2 , an increase by a factor of 7 from 2006, and thus does not scale linearly with fuel emission mass. This is due to non-uniform regional increase in air traffic and different sensitivities for contrail radiative forcing in different regions.CAM5 simulations indicate that negative radiative forcing induced by the indirect effect of aviation sulfate aerosols on liquid clouds in 2050 can be as large as −160 mW m −2 , an increase by a factor of 4 from 2006. As a result, the net 2050 radiative forcing of contrail cirrus and aviation aerosols may have a cooling effect on the planet. Aviation sulfate aerosols emitted at cruise altitude can be transported down to the lower troposphere, increasing the aerosol concentration, thus increasing the cloud drop number concentration and persistence of low-level clouds. Aviation black carbon aerosols produce a negligible net forcing globally in 2006 and 2050 in this model study.Uncertainties in the methodology and the modeling are significant and discussed in detail. Nevertheless, the projected percentage increase in contrail radiative forcing is important for future aviation impacts. In addition, the role of aviation aerosols in the cloud nucleation processes can greatly influence on the simulated radiative forcing from aircraft-induced cloudiness and even change its sign. Future research to confirm these results is necessary.

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Section: Discussionsupporting

confidence: 78%

Section: Modeling Framework and Background Meteorologymentioning

confidence: 99%

Section: Modeling Framework and Background Meteorologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Simulated 2050 aviation radiative forcing from contrails and aerosols

Chen

Gettelman

2016

Atmos. Chem. Phys.

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“…This is a valid approach as long as the climate response to the disturbances is about linear. Gettelman and Chen (2013) and Chen and Gettelman (2013) were able to reduce the climate noise using a 20-year climate model (CAM5) simulation nudged to the pressure, winds and atmospheric and sea surface temperatures from a previous 1-year simulation. In order to quantify the effects of this nudging, one would need comparisons with and without nudging.…”

Section: U Schumann Et Al: Dehydration Effects From Contrails In a mentioning

confidence: 99%

Dehydration effects from contrails in a coupled contrail–climate model

et al. 2015

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Abstract. The uptake of water by contrails in icesupersaturated air and the release of water after ice particle advection and sedimentation dehydrates the atmosphere at flight levels and redistributes humidity mainly to lower levels. The dehydration is investigated by coupling a plumescale contrail model with a global aerosol-climate model. The contrail model simulates all the individual contrails forming from global air traffic for meteorological conditions as defined by the climate model. The computed contrail cirrus properties compare reasonably with theoretical concepts and observations. The mass of water in aged contrails may exceed 10 6 times the mass of water emitted from aircraft. Many of the ice particles sediment and release water in the troposphere, on average 700 m below the mean flight levels. Simulations with and without coupling are compared. The drying at contrail levels causes thinner and longer-lived contrails with about 15 % reduced contrail radiative forcing (RF). The reduced RF from contrails is on the order of 0.06 W m −2 , slightly larger than estimated earlier because of higher soot emissions. For normal traffic, the RF from dehydration is small compared to interannual variability. A case with emissions increased by 100 times is used to overcome statistical uncertainty. The contrails impact the entire hydrological cycle in the atmosphere by reducing the total water column and the cover by high-and low-level clouds. For normal traffic, the dehydration changes contrail RF by positive shortwave and negative longwave contributions on the order of 0.04 W m −2 , with a small negative net RF. The total net RF from contrails and dehydration remains within the range of previous estimates.

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Reassessing properties and radiative forcing of contrail cirrus using a climate model

2016

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Contrail cirrus is the largest known component contributing to the radiative forcing associated with aviation. Despite major advances simulating contrail cirrus, their microphysical and optical properties and the associated radiative forcing remain largely uncertain. We use a contrail cirrus parameterization in a global climate model which was extended to include a microphysical two‐moment scheme. This allows a more realistic representation of microphysical processes, such as deposition and sedimentation, and therefore of the microphysical and optical properties of contrail cirrus. The simulated contrail microphysical and optical properties agree well with in situ and satellite observations. As compared to estimates using an older version of the contrail cirrus scheme, the optical depth of contrail cirrus is significantly higher, particularly in regions with high air traffic density, due to high ice crystal number concentrations on the main flight routes. Nevertheless, the estimated radiative forcing for the year 2002 supports our earlier results. The global radiative forcing of contrail cirrus for the year 2006 is estimated to be 56mW/m2. A large uncertainty of the radiative forcing estimate appears to be connected with the, on average, very small ice crystal radii simulated in the main air traffic areas, which make the application of a radiative transfer parameterization based on geometric optics questionable.

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Simulated radiative forcing from contrails and contrail cirrus

Cited by 57 publications

References 40 publications

Simulated 2050 aviation radiative forcing from contrails and aerosols

Simulated 2050 aviation radiative forcing from contrails and aerosols

Dehydration effects from contrails in a coupled contrail–climate model

Reassessing properties and radiative forcing of contrail cirrus using a climate model

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